Writing instrument refill



FIG. 1 is a perspective view showing our new design for a writing instrument refill;

FIG. 2 is an elevational view of the writing instrument refill of FIG. 1;

FIG. 3 is a top plan view of the writing instrument refill of FIG. 1; and,

FIG. 4 is a bottom plan of the writing instrument refill of FIG. 1.

The dashed lines are of illustrative purposes only and form no part of the claimed design. 

The ornamental design for a writing instrument refill, as shown and described. 